1. Field of the Invention
The present invention relates to a hybrid drive apparatus and a controller for the hybrid drive apparatus. More particularly, the present invention relates to a hybrid drive apparatus that is configured to allow a vehicle to use only an electric motor as a drive power source to travel in motor drive mode when rotational driving of an internal combustion engine is stopped, and relates to a controller for the hybrid drive apparatus.
2. Description of Related Art
Conventionally-known hybrid vehicles use an internal combustion engine and a motor generator (an electric motor) as a drive power source to rotate an output shaft of the internal combustion engine. The rotations of the output shaft activate an oil pump to supply lubricant from the oil pump to a power transmission mechanism. The conventionally-known hybrid vehicles are configured to transmit a rotational torque of the motor generator to the oil pump to supply lubricant from the oil pump to the power transmission mechanism, when the vehicle travels in an electric vehicle drive mode (EV drive mode) in which rotational driving of the internal combustion engine is stopped.
For example, one of the conventionally-known hybrid vehicles uses a planetary gear mechanism as the power transmission mechanism to distribute an output of the internal combustion engine to the drive wheels and to the motor generator. When the vehicle travels in a hybrid drive mode (HV drive mode), a rotational torque of the output shaft of the internal combustion engine activates the oil pump. When the vehicle travels in the motor drive mode (EV drive mode), a rotational torque of the motor generator forces the output shaft of the internal combustion engine to rotate to activate the oil pump.
However, in a case where the motor generator is kept driven while the vehicle travels in the motor drive mode (EV drive mode), this causes the amount of battery consumed by the motor generator to excessively increase. This can possibly cause some problems, such as reducing a traveling distance of the vehicle in the EV drive mode.
Thus, a hybrid drive apparatus disclosed in Japanese Patent Application No. 2008-238837 (JP-A-2008-238837) is configured to determine whether the power transmission mechanism needs to be supplied with lubricant based on a distance that the vehicle has travelled in the EV drive mode in which the rotational driving of the internal combustion engine is stopped, or based on an amount of electrical energy stored in the capacitor. If the hybrid drive apparatus determines that the power transmission mechanism needs to be supplied with lubricant, the hybrid drive apparatus drives the internal combustion engine to rotate.
The hybrid drive apparatus disclosed in JP-A-2008-238837 activates the oil pump at an appropriate timing, when the vehicle is in the EV drive mode, to prevent the planetary gear mechanism which serves as the power transmission mechanism under no lubrication condition from seizure or other problems. It allows the power transmission mechanism to be supplied with the lubricant intermittently. The hybrid drive apparatus needs not to activate the oil pump constantly. It results in minimizing the amount of battery consumed by the motor generator, and therefore results in an increase in traveling distance of the vehicle in the EV drive mode.
However, such a conventional hybrid drive apparatus as disclosed above has to drive the motor generator to rotate the output shaft of the internal combustion engine at a rotational speed at which the oil pump discharges oil, in order for the oil to be supplied to the power transmission mechanism.
As the output shaft of the internal combustion engine rotates at a lower rotational speed, a larger amount of oil leaks from the oil pump, and thus the oil pump has lower discharge efficiency. Therefore, the rotational speed of the output shaft needs to be increased approximately to the idling speed at which the oil pump supplies a sufficient amount of oil to the power transmission mechanism.
The motor generator is kept driven for a certain period of time until the output shaft of the internal combustion engine rotates at a rotational speed at which the oil pump can discharge a sufficient amount of oil. Accordingly, the amount of battery consumed by the motor generator may undesirably increase.